Simultaneous determination of aliphatic, aromatic and heterocyclic biogenic amines without derivatization by capillary electrophoresis and application in beer analysis.

Biogenic amines (BAs) play significant roles in indicating human health or food quality. Aiming to simultaneously determine three structures (aliphatic, aromatic and heterocyclic) of underivatized BAs, we explored a simple and rapid capillary electrophoresis (CE) method only coupled with conventional UV detector for the separation of thirteen key BAs. The strategy is to choose a UV absorbing probe as co-ion in the background electrolyte (BGE), and different BAs could be characterized by positive or negative peaks according to the fact that their UV absorptivity coefficients at a certain wavelength are better or worse than that of the UV absorbing probe. After the detailed investigation of critical parameters as pH, the concentration of Imidazole (Im) and α-cyclodextrin (α-CD), the optimized BGE consisted of 12.0mmol/L Im as the UV probe and 10.0mmol/L α-CD as the additive (at pH 4.50 adjusted with acetic acid). With such condition, the targets of thirteen BAs were baseline separated in 9.0min and appeared at nine positive peaks and four negative peaks at 200nm. The obtained LODs and LOQs (S/N=3 or 10) were in the range of 0.36-3.67 and 1.2-12.2µmol/L, respectively. The interday RSDs of migration time and peak area were less than 0.7% and 4.7% (n=6), respectively. To the best of our knowledge, this is the first report on separating diverse structures of BAs by using Im as UV absorbing probe. The thirteen BAs were simultaneously detected by direct and indirect UV detection in a CE process. To verify the applicability, this method was used to analyze BAs in commercial beer samples. The recoveries of all BAs except carnosine (not identified by the interference) ranged from 70.4 to 119.6%, and four aliphatic and aromatic amines were satisfactorily identified and quantified.

Determination of Inorganic Anions in Seawater Samples by Ion Chromatography with Ultraviolet Detection Using Monolithic Octadecylsilyl Columns Coated with Dodecylammonium Cation.

A fast and sensitive ion chromatographic method for the simultaneous determinations of six inorganic anions [iodate (IO3-), bromate (BrO3-), bromide (Br-), nitrite (NO2-), nitrate (NO3-), and iodide (I-)] in seawater is described using dodecylammonium (DA+)-coated monolithic octadecylsilyl (ODS) columns, a concentrated aqueous NaCl mobile phase containing dodecylammonium chloride (DAC), and a UV detector. The DA+-coated monolithic ODS columns show greater retention for iodate and weaker retention for iodide, compared to dilauryldimethylammonium (DDA+)-coated monolithic ODS columns. Six anions were determined within 12 min with baseline separation without interferences by matrix ions, such as Cl- and SO42-, in seawater, compared to a DA+-coated particulate ODS column (it took 25 min per sample) obtained previously. The detection limits (DLs) were comparable to the DA+-coated particulate ODS column: IO3- (7.7 µg L-1), BrO3- (20), Br- (88), NO2- (0.9), NO3- (1.9), and I- (0.9) with a 100-µL sample injection. A larger sample volume injection lowered the DLs of IO3-, BrO3-, and I-. The good performance was maintained for ca. 2 years examined. The robust IC system developed in the present work was successfully applied to real seawater samples without sample dilution in the recovery rates of 93 - 104% for all ions.

Pressure-assisted electrokinetic injection stacking for verteporfin drug to achieve highly sensitive enantioseparation and detection in artificial urine by capillary electrophoresis.

Pressure-assisted electrokinetic injection (PAEKI) was applied for negatively charged verteporfin (VER) overloading and inline stacking, which targeted highly sensitive enantioseparation by CE. The essential step of PAEKI is a constant pressure used to counterbalance the electroosmotic flow (EOF), consequently, the large amount of analyte could be permitted into capillary and concentrated at the motionless boundary of the sample zone and background electrolyte (BGE). Aiming to know the balance, the velocity of the whole BGE in capillary by the impetus of pressure (0.2-2.0psi), and the velocity of EOF depending on the length of sample plug and voltage (5.0-20kV) was investigated, respectively. The velocity of bulk flow in capillary has good linearity with the pressure or applied voltage. Through the pattern of EOF marked peak and analyte peaks (dissolved in pure water), the constant pressure (0.8psi) vs. the added voltage (-10.3kV) during PAEKI was confirmed to immobilize the bulk flow of BGE, thus the sample injection time could sustain 2.0min without compromising separation efficiency. The obtained LOD (S/N=3) of each isomer at UV detection (428nm) was around 10.3µg/L, which was improved to 116 and 39-fold in comparison with normal hydrodynamic injection (HDI) and electrokinetic injection (EKI). The LOD is far below the reported value with LIF detection of VER. The RSD (n=5) of migration time and peak area was, respectively, around 3.5% and 5.7% for the proposed PAEKI method. Finally, PAEKI was used for the detection of VER in artificial urine to investigate the matrix interference.

Can neutral analytes be concentrated by transient isotachophoresis in micellar electrokinetic chromatography and how much?

Transient isotachophoresis (tITP) is a versatile sample preconcentration technique that uses ITP to focus electrically charged analytes at the initial stage of CE analysis. However, according to the ruling principle of tITP, uncharged analytes are beyond its capacity while being separated and detected by micellar electrokinetic chromatography (MEKC). On the other hand, when these are charged micelles that undergo the tITP focusing, one can anticipate the concentration effect, resulting from the formation of transient micellar stack at moving sample/background electrolyte (BGE) boundary, which increasingly accumulates the analytes. This work expands the enrichment potential of tITP for MEKC by demonstrating the quantitative analysis of uncharged metal-based drugs from highly saline samples and introducing to the BGE solution anionic surfactants and buffer (terminating) co-ions of different mobility and concentration to optimize performance. Metallodrugs of assorted lipophilicity were chosen so as to explore whether their varying affinity toward micelles plays the role. In addition to altering the sample and BGE composition, optimization of the detection capability was achieved due to fine-tuning operational variables such as sample volume, separation voltage and pressure, etc. The results of optimization trials shed light on the mechanism of micellar tITP and render effective determination of selected drugs in human urine, with practical limits of detection using conventional UV detector.

Role of counter-ions in background electrolyte for the analysis of cationgenic weak electrolytes and amino acids in neutral aqueous solutions by capillary electrophoresis with electrokinetic injection.

We elucidated theoretically and experimentally that counter-ions in background electrolyte (BGE) play a role of booster for electrokinetic injection (EKI) for the determination of cationgenic weak electrolytes and amino acids in neutral aqueous solutions using capillary electrophoresis (CE). The pH change in the sample solution caused by the migration of counter-ions resulted in the increase of analyte mobility and hence the increase of the amount of analyte injected into the capillary. This type of EKI was named as counter-ion boosted EKI. Using the counter-ion boosted EKI-capillary zone electrophoresis (CZE), the limit of detections (LODs, S/N=3) for creatinine (4.8nM) and l-histidine (9.0nM) were lowest ever achieved by CE with UV detection. The RSDs (n=3) of the migration time for creatinine and l-histidine were obtained as 0.35% and 0.34%, for peak areas of 13% and 12%, and for peak heights of 12% and 8.5%, respectively. The concentrations of creatinine and l-histidine in a urine sample obtained by the proposed method were within those reported with a good recovery.

DNA aggregation and cleavage in CGE induced by high electric field in aqueous solution accompanying electrokinetic sample injection.

The phenomenon of peak area decrease due to high injection voltage (Vinj , e.g. 10-30 kV, 200-600 V/cm in the 50 cm capillary) was found in the analysis of very dilute DNA fragments (<0.2 mg/L) by using high-sensitive electrokinetic supercharging-CGE. The possibility of DNA cleavage in aqueous solution was suggested, in addition to the aggregation phenomenon that is already known. The analysis of intentionally voltage-affected fragments (at 200 V/cm) also showed decreased peak areas depending on the time of the voltage being applied. Computer simulation suggested that a high electric field (a few kV/cm or more) could be generated partly between the electrode and the capillary end during electrokinetic injection (EKI) process. After thorough experimental verification, it was found that the factors affecting the damage during EKI were the magnitude of electric field, the distance between tips of electrode and capillary (De/c ), sample concentration and traveling time during EKI in sample vials. Furthermore, these factors are correlating with each other. A low conductivity of diluted sample would cause a high electric field (over a few hundred volts per centimeter), while the longer De/c results in a longer traveling time during EKI, which may cause a larger degree of damage (aggregation and cleavage) on the DNA fragments. As an important practical implication of this study, when the dilute DNA fragments (sub mg/L) are to be analyzed by CGE using EKI, injection voltage should be kept as low as possible.

Electrokinetic supercharging preconcentration prior to CGE analysis of DNA: sensitivity depends on buffer viscosity and electrode configuration.

Aiming to high sensitivity DNA analysis by CGE, electrokinetic supercharging (EKS) approach was adopted in this article. EKS is known as an online preconcentration technique that combines electrokinetic sample injection (EKI) with transient ITP (tITP). Herein, two factors of buffer viscosity and electrode configuration were studied to further improve EKS performance. An ultralow-viscosity Tris-Boric acid-EDTA (TBE) buffer solution, consisted of 2% low-molecular-weight hydroxypropyl methyl cellulose (HPMC) and 6% mannitol and with pH 8.0 adjusted by boric acid, was applied. The boric acid would make a complex with mannitol and generates borate polyanion, which acts as the leading ion for tITP process. The new electrode configuration, a Pt ring around capillary, was modified on Agilent CE system to lead large amount sample introduction during EKS. The standard DNA sample of φX174/HaeIII digest was used to evaluate the qualitative and quantitative abilities of the proposed strategy. The 170,000-fold highly diluted sample at concentration of 3.0 ng/mL was enriched by EKS and detected by normal UV detection method. The obtained LOD of the weakest peak of 72 bp fragment was around 7.7 pg/mL, apparently improved more than 10,000-fold in comparison with conventional CGE with UV detection.

Simultaneous determination of pyridine-triphenylborane anti-fouling agent and its degradation products in paint-waste samples using capillary zone electrophoresis with field-amplified sample injection.

We proposed a capillary zone electrophoresis (CZE) procedure using field-amplified sample injection (FASI) for the simultaneous determination of pyridine-triphenylborane (PTPB) and its degradation products: diphenylborinic acid (DPB), phenylboronic acid (MPB), and phenol. The LODs for PTPB, DPB, MPB, and phenol were, respectively, 0.85, 0.88, 44, and 28 µg L(-1). The RSDs (n = 4) for the analytes listed above were in respective ranges of 6.2 - 14, 5.9 - 10, and 0.49 - 0.62% for the peak area, peak height, and migration time. The compounds were extracted from paint-waste samples collected from shipyards using a siliga-gel column. The extract was dissolved with acetonitrile containing 1% (v/v) pyridine. The samples were then analyzed using CZE, revealing respective concentrations of 0.076 - 0.53, 0.015 - 0.36, 1.7 - 22, and 1.2 - 13 µg g(-1). The proposed FASI-CZE method is a simple and promising procedure that is expected to be useful for the determination of PTPB and its degradation products in paint wastes.

Determination of nitrite, nitrate, bromide, and iodide in seawater by ion chromatography with UV detection using dilauryldimethylammonium-coated monolithic ODS columns and sodium chloride as an eluent.

A method was developed for determination of inorganic anions, including nitrite (NO(2)(-)), nitrate (NO(3)(-)), bromide (Br(-)), and iodide (I(-)), in seawater by ion chromatography (IC). The IC system used two dilauryldimethylammonium bromide (DDAB)-coated monolithic ODS columns (50 × 4.6 mm i.d. and 100 × 4.6 mm i.d.) connected in series for separation of the ions. Aqueous NaCl (0.5 mol/L; flow rate, 3 mL/min) containing 5 mmol/L phosphate buffer (pH 5) was used as the eluent, and detection was with a UV detector at 225 nm. The monolithic ODS columns were coated and equilibrated with a 1-mmol/L DDAB solution (in H(2)O/methanol, 90:10 v/v). The hydrophilic ions (NO(2)(-), NO(3)(-), and Br(-)) were separated within 3 min and the retention time of I(-) was 16 min. No interferences from matrix ions, such as chloride and sulfate ions, were observed in 35 ‰ artificial seawater. The detection limits were 0.6 µg/L for NO(2)(-), 1.1 µg/L for NO(3)(-), 70 µg/L for Br(-), and 1.6 µg/L for I(-) with a 200-µL sample injection. The performance of the coated columns was maintained without addition of DDAB in the eluent. The IC system was successfully applied to real seawater samples with recovery rates of 94-108 % for all ions.

[Analysis of aliphatic carboxylic acids in anaerobic digestion process waters by ion-exclusion chromatography].

The analysis of seven aliphatic carboxylic acids (formic, acetic, propionic, iso-butyric, n-butyric, iso-valeric and n-valeric acid) in anaerobic digestion process waters for biogas production was examined by ion-exclusion chromatography with dilute acidic eluents (benzoic acid, perfluorobutyric acid (PFBA) and sulfuric acid) and non-suppressed conductivity/ultraviolet (UV) detection. The columns used were a styrene/divinylbenzene-based strongly acidic cation-exchange resin column (TSKgel SCX) and a polymethacrylate-based weakly acidic cation-exchange resin column (TSKgel Super IC-A/C). Good separation was performed on the TSKgel SCX in shorter retention times. For the TSKgel Super IC-A/C, peak shape of the acids was sharp and symmetrical in spite of longer retention times. In addition, the mutual separation of the acids was good except for iso- and n-butyric acids. The better separation and good detection was achieved by using the two columns (TSKgel SCX and TSKgel Super IC-A/C connected in series), lower concentrations of PFBA and sulfuric acid as eluents, non-suppressed conductivity detection and UV detection at 210 nm. This analysis was applied to anaerobic digestion process waters. The chromatograms with conductivity detection were relatively simpler compared with those of UV detection. The use of two columns with different selectivities for the aliphatic carboxylic acids and the two detection modes was effective for the determination and identification of the analytes in anaerobic digestion process waters containing complex matrices.

A novel hybrid mode of sample injection to enhance CZE sensitivity for simultaneous determination of a pyridine-triphenylborane anti-fouling agent and its degradation products.

We developed a novel hybrid sample injection mode (HSIM) that presents the combination of electrokinetic injection and vacuum injection to enhance detection sensitivity in CZE. Samples were introduced using both vacuum and electrokinetic injections simultaneously, with a water plug injected into the capillary prior to sample introduction (i.e. similarly to field-amplified sample injection, FASI). Using a sample mixture containing an anti-fouling agent applied to ship hulls, pyridine-triphenylborane and its degradation products (diphenylborinic acid, phenylboronic acid, and phenol) dissolved in ACN, the length of water plug, time, and voltage for sample introduction were optimized. The signal intensity (peak height) was found to be up to a 30-fold increased using HSIM by applying 4 kV for 4 s at the inlet end of the capillary as the cathode with supplementary vacuum in comparison with only vacuum injection for 4 s. The LODs (at a S/N of 3) for pyridine-triphenylborane, diphenylborinic acid, phenylboronic acid, and phenol were 0.88, 1.0, 21, and 23 µg/L, respectively. At the level of 0.04 mg/L, the RSDs (n=4, intra-day) for the above analytes were in the ranges of 1.9-11, 4.3-9.2, and 0.34-0.66% for peak area, peak height, and migration time, respectively. The HSIM is a simple and promising procedure useful for enhancing the sensitivity for both low-and high-mobility ions in CZE.

Electrokinetic supercharging with a system-induced terminator and an optimized capillary versus electrode configuration for parts-per-trillion detection of rare-earth elements in CZE.

A further improvement of electrokinetic supercharging (EKS) methodology has been proposed, with the objective to enhance the sensitivity of the conventional CZE-UV method down to a single-digit part per trillion (ppt) level. The advanced EKS procedure is based on a novel phenomenon displaying the formation of a zone with an increased concentration of the hydrogen ion, capable to perform the function of a terminator, behind the sample zone upon electrokinetic injection. In combination with a visualizing co-ion of BGE, protonated 4-methylbenzylamine, acting as the leading ion, such system-induced terminator a effected the transient ITP state to efficiently concentrate cationic analytes prior to CZE. Furthermore, to amass more analyte ions within the effective electric field at the injection stage, a standard sample vial was replaced with an elongated vial that allowed the sample volume to be increased from 500 to 900 µL. Alongside, this replacement made the upright distance between the electrode and the capillary tips prolonged to 40.0 mm to achieve high-efficiency electrokinetic injection. The computer simulation was used for profiling analyte concentration, pH, and field strength in order to delineate formation of the terminator during sample injection. The proposed preconcentration strategy afforded an enrichment factor of 80,000 and thereby the LODs of rare-earth metal ions at the ppt level, e.g. 0.04 nM (6.7 ng/L) for erbium(III).

Another approach toward over 100,000-fold sensitivity increase in capillary electrophoresis: electrokinetic supercharging with optimized sample injection.

Electrokinetic supercharging (EKS) is a powerful and practical method for multifold in-line concentration of various analytes prior to capillary electrophoresis (CE) analysis. However, a problem of insufficient sensitivity has always existed when trace analyte quantification by EKS-CE is a target, especially when coupled with conventional detectors. Normally this requires a greatly increased amount of analyte injected without separation degradation. In this contribution, we have shown that it is possible to substantially improve analyte loading and hence CE method detectability by modifying sample introduction configuration. The volume of sample vial was increased (from typical 500 µL to 17 mL), the common wire electrode was replaced by a ring electrode, and the sample solution was stirred. With these alterations, more analyte ions are accumulated within the effective electric field during electrokinetic injection and then maintained as focused zones due to transient isotachophoresis. The versatility of the customized EKS-CE approach for sample concentration was demonstrated for a mixture of seven rare-earth metal ions with an enrichment factor of 500 000 giving detection limits at or below 1 ng/L. These detection limits are over 100 000 times better than can be achieved by normal hydrodynamic injection, 1000 times better than the sensitivity thresholds of inductively coupled plasma atomic emission spectrometry (ICP-AES), and even close to those of inductively coupled plasma mass spectrometry (ICPMS).

Investigation of the pH gradient formation and cathodic drift in microchip isoelectric focusing with imaged UV detection.

This paper reports the protein analysis by using microchip IEF carried on an automated chip system. We herein focused on two important topics of microchip IEF, the pH gradient and cathodic drift. The computer simulation clarified that the EOF could delay the establishment of pH gradient and move the carrier ampholytes (CAs) to cathode, which probably caused a cathodic drift to happen. After focusing, the peak positions of components in a calibration kit with broad pI were plotted against their pI values to know the actual pH gradient in a microchannel varying time. It was found that the formed pH gradient was stable, not decayed after readily steady state, and migrated to cathode at a rate of 10.0 µm/s that determined by the experimental conditions such as chip material, internal surface coating and field strength. The theoretical pH gradient was parallel with the actual pH gradient, which was demonstrated in two types of microchip with different channel lengths. No compression of pH gradient was observed when 2% w/v hydroxypropyl methyl cellulose was added in sample and electrolytes. The effect of CAs concentration on current and cathodic drift was also explored. With the current automatic chip system, the calculated peak capacity was 23-48, and the minimal pI difference was 0.20-0.42 for the used single channel microchip with the effective length of 40.5 mm. The LOD for the analysis of CA-I and CA-II was around 0.32 µg/mL by using normal imaged UV detection, the detected amount is ca. 0.07 ng.

Band-broadening suppressed effect in long turned geometry channel and high-sensitive analysis of DNA sample by using floating electrokinetic supercharging on a microchip.

A featured microchip owning three big reservoirs and long turned geometry channel was designed to improve the detection limit of DNA fragments by using floating electrokinetic supercharging (FEKS) method. The novel design matches the FEKS preconcentration needs of a large sample volume introduction with electrokinetic injection (EKI), as well as long duration of isotachophoresis (ITP) process to enrich low concentration sample. In the curved channel [ approximately 45.6 mm long between port 1 (P1) and the intersection point of two channels], EKI and ITP were performed while the side port 3 (P3) was electrically floated. The turn-induced band broadening with or without ITP process was investigated by a computer simulation (using CFD-ACE+ software) when the analytes traveling through the U-shaped geometry. It was found that the channel curvature determined the extent of band broadening, however, which could be effectively eliminated by the way of ITP. After the ITP-stacked zones passed the intersection point from P1, they were rapidly destacked for separation and detection from ITP to zone electrophoresis by using leading ions from P3. The FEKS carried on the novel chip successfully contributed to higher sensitivities of DNA fragments in comparison with our previous results realized on either a single channel or a cross microchip. The analysis of low concentration 50 bp DNA step ladders (0.23 mugml after 1500-fold diluted) was achieved with normal UV detection at 260 nm. The obtained limit of detections (LODs) were on average 100 times better than using conventional pinched injection, down to several ngml for individual DNA fragment.

Contribution of Ni KLL Auger electrons to the probing depth of the conversion electron yield measurements.

The averaged attenuation length of emitted electrons with the conversion electron yield (CEY) method was evaluated for Ni films with the x-rays below and above the Ni K absorption edge. The evaluated attenuation length was 13.1 nm with the x-rays below the Ni K absorption edge, and it became 24.0 nm with the contribution of Ni KLL Auger electrons that had the attenuation length of 78.1 nm. The probing depth of the CEY measurements are determined both the penetration depth of x-rays and the attenuation length of emitted electrons, and the modification of the probing depth was investigated with the grazing incidence condition. The glancing angle dependence of the CEY was compared with the model calculation, and the probing depth of around 1.6 nm was realized under the total reflection condition. The probing depth was controlled from 1.6 nm to the attenuation length by changing the glancing angle.

Focusing of anionic micelles using sample-induced transient isotachophoresis: computer simulation and experimental verification in MEKC.

The specific phenomenon of high-salt micelle focusing used as a preconcentration method for uncharged solutes in MEKC has been interpreted in terms of complementary transient isotachophoresis (tITP) process. High matrix chloride can focus anionic SDS micelles not only due to a field-enhanced effect but also by creating the tITP state in which chloride acts as a leading ion. The latter micelle-enrichment event was simulated by SIMUL software in order to understand tITP conditions under which micelle stacking can be expected to occur. Specifically, effects of chloride matrix concentration and the nature of BGE co-ion, performing a role of terminating ion, were explored. A greater extent of micelle stacking was observed at a higher chloride concentration in borate than in phosphate buffer system. This proof-of-principle simulation result was confirmed in real experiments using metal-based chemotherapeutic drugs. It was concluded that analyte enrichment requires prolonged interaction with the micelle, which is feasible at a proper ratio between sample matrix and BGE co-ion concentrations.

Sensitive profiling of biogenic amines in urine using CE with transient isotachophoretic preconcentration.

A transient ITP-CZE system is proposed for the determination of biogenic amines in urine. The complete separation and identification of dopamine, tyramine (TA), tryptamine (T), serotonin, epinephrine, norepinephrine, and normetanephrine have been achieved in a twofold diluted urine sample (in which the analytes were below the LODs by normal CZE). The tITP preconcentration conditions were created by introducing a 30 mM solution of NaOH, containing 0.1% hydroxypropylcellulose (pH 6.5 adjusted with MES), and 0.1 M HCl before and after the sample zone to work as leading and terminating electrolytes, respectively. This allowed the LODs of direct UV absorption detection to be decreased down to the 10(-8) M level that is comparable with the sensitivity thresholds of LIF detection or inline SPE-CE. The RSDs of migration time and peak area for real-biofluid analysis were in the range of 0.1-4.5% and 0.8-16% (n=3), respectively. Quantification of dopamine, TA, T, and serotonin was performed using internal calibration. To the best of our knowledge, this is the first report on probing urinal biogenic amines and their metabolites by tITP-CZE.

Electrokinetic sample injection for high-sensitivity CZE (part 2): improving the quantitative repeatability and application of electrokinetic supercharging-CZE to the detection of atmospheric electrolytes.

Electrokinetic supercharging (EKS) is defined as a technique that combines electrokinetic sample injection with transient ITP. Quantitative repeatability of EKS-CZE and the other CE methods using electrokinetic sample injection process is usually inferior in comparison with the CE methods using hydrodynamic or hydrostatic injection. This is due to some effects, such as the temperature change and the convection of the sample solution in the reservoir, as well as the change of the distance between an electrode and a capillary end (D(ec)). In particular, we have found that the D(ec) change might most seriously affect the repeatability, especially when the electrode is a thin Pt wire that could be unintentionally bent during sampling. By using a Teflon spacer to fix D(ec) to 1.1 mm, the RSD of peak area (n=5) was decreased from 20 to 3.4% in EKS-CZE for several metal cations. This D(ec) dependence of the sample amount injected was supported by computer simulation using CFD-ACE+ software. The improved repeatability (down to 5.1% at n=5, averaged RSD for Co(2+), Li(+), Ni(2+), Zn(2+) and Pb(2+)) was also experimentally attained by increasing the D(ec) to ca. 20 mm, which was also effective to obtain high sensitivity. Since the temperature and the convection effects on the repeatability are comparatively small in a proper laboratory environment, these effects were estimated from the EKS-CZE experiments using conditions such as warming and agitating the sample solution during EKS process. Finally, EKS-CZE was applied to the detection of ions from atmospheric electrolytes in high-purity water exposed to ambient air for 2 h. The microgram per liter levels of anions (chloride, sulfate, nitrate, formate, acetate and lactate) and cations (ammonium, calcium, sodium and magnesium) could be detected using conventional UV detector.

[Preconcentration and separation of DNA fragments based on microchip electrophoresis].

An online preconcentration method, electrokinetic supercharging (EKS) was used for the enrichment of DNA fragments based on microchip electrophoresis (MCE). EKS is a process that combines electrokinetic injection (EKI) with transient isotachophoresis (tITP). The results demonstrated that the large volume of low concentration sample could be introduced, preconcentrated, and eventually separated on a single channel microchip with the whole length of 40.5 mm. The limit of detection (S/N = 3) of DNA fragments was around 0.07 mg/L, effectively improved 40-fold by EKS preconcentration with the normal UV detection at 260 nm. Some important parameters for enhancing preconcentration and qualitative analysis were examined.